SCIENCE. 



[Vol. XVI. No. 4C0 



ing procured from foul or stagnant water. In this case the opin- 

 ion of M. Dutertre, that the liver of poisonous mussels is the seat 

 of disease and the generator of the poisonous leucomaine, seems 

 confirmed; but I cannot agree with the French observer, that the 

 disease is never the result of the poisonous nature of the food of 

 the mussel. I have read all, or nearly all, the cases of mussel- 

 poisoning on record, and I gather from such details as are given 

 with respect to the places in which the mussels were found that 

 they were in contact with sewage or stagnant water." 



EECENT THEORIES OF GEOMETRICAL ISOMERISM.' 



The histologist places a section of organized tissue upon the 

 stage of his microscope, and studies its structure. He reports upon 

 the cells and their contents, for he has seen them, but he has not 

 detected the molecule. The smallest discernible particle was 

 probably an aggregate of at least a million molecules of elaborate 

 structure, permeated by many times as many molecules of simpler 

 composition. 



The actual configuration of atoms in the molecule, the bonds 

 by which they are united, the mechanism which effects transfor- 

 mations from one form to another, and, indeed, the very exist- 

 ence of molecules, are subjects which do not belong to the world 

 of sight. • It is not likely that any human eye, with the most per- 

 fect optical instruments, will ever penetrate these secrets of an 

 unseen world. 



But the many unseen worlds are favorite hunting-grounds of 

 science. The imagination of the geologist sees successive strata 

 in regular order or thrown into folds, where the rocks are hidden 

 from the uninitiated by drift, soil, and forest, or even where they 

 were long since removed by erosion. The astronomer, having 

 discovered a simple law controlling the motions of the planets, 

 pursues them with the formulas of dynamics and perturbations, 

 until the unexplained residuals of motion lead him to the very spot 

 occu])ied by Neptune. The biologist experiments upon the vitality 

 of invisible germs, but the chemist reasons upon the elements 

 that make up molecules of which these germs consist. He recog- 

 nize? atoms having simple, double, triple, and quadruple power 

 of union. Whatever be the nature of this union, the ■'bonds" 

 are as real as ever held prisoner to Roman soldier. The structural 

 formulas which characterize the language of modern chemistry 

 ■express the fact that each atom is specially related to a certain one 

 •or more other atoms, with scarcely the least claim in regard to 

 ■distance or direction. 



The doctrine of valence and types prepared the way for the 

 more elaborate doctrines embodied in structural formulas, which 

 so admirably explain numerous re-actions and isomers. Such 

 is our ignorance of the actual relations of the atoms in space, that 

 no photographs of geometrical isomers can be offered for inspec- 

 tion; yet certain working hypotheses of their configuration, which 

 were received for some years with great reserve, have recently 

 had such influence in shaping the current of research in organic 

 chemistry, that they are well worth our attention at this hour. 



When the quadrivalent character of carbon was distinctly recog- 

 nized, as in CHj, it was (irobably not long before the regular 

 tetrahedron often occurred to thinking minds as a suitable repre- 

 sentation. If CH4 thus represents the outline of a regular tetra- 

 hedron, it must not be supposed that the actual form is changeless, 

 but rather that the mean positions of the hydrogen atoms are at 

 the angles. In substitution products, we may think of the several 

 radicles oscillating about mean positions that are at unequal dis- 

 tances from each other, the mutual attraction of the most unlike 

 groups bringing them somewhat towards each other. The condi- 

 tions in the two forms (see below) are so far identical that the mean 

 mutual distance of any pair of groups will be the same in both. 

 The difference would not be likely to make one form more easily 

 soluble or volatile than the other. The usual means of distin- 

 guishing isomers may fail. Ordinary methods of fractional distil- 

 lation or precipitation are alike useless to distinguish tweedledum 

 and tweedledee. A most delicate instrument, capable of feeling 

 the slightest resistance to the vibrations of luminiferous ether, is 



' Abstract of an address before the American Association for the Advance- 

 ment of Science, by Robert B. Warder, vice-president of Section C. 



found in a ray of polarized light. When such a ray passes through 

 the asymmetric molecule, it is probable that greater resistance 

 will be met in some one plane than in another, and thus the plane 

 of polarization is slightly turned. In a fluid aggregate, a ray 

 will meet successive molecules in all possible positions; and while 

 these must have unequal effects, — sometimes, perhaps, in oppo- 

 site directions, — the mean result for a large number will always 

 be the same. 



Le Bel and van't Hoff were the first to state clearly (and inde- 

 pendently) the fundamental principles upon which this branch of 

 chemical investigation has been developed. In the first place, 

 when carbon is linked with four different radicles, two isomers will 

 usually result, the forms of the molecule being related to each 

 other as an object to its image in a plane mirror. These isomers 

 closely resemble each other in most physical and chemical prop- 

 erties. Two such atoms may be represented by tetrahedrons, 

 united at the corners, where it is important to note the cyclical 

 order of the radicles attached to each carbon atom as seen from 

 that atom itself. 



Our theory must conform, however, to the observed facts; other- 

 wise we may either be overwhelmed with a multitude of imaginary 

 isomers, or we may be unable to account for aU that are discov- 

 ered. The following principle (which has been known as "van't 

 Hoff's second hypothesis') is supported by many facts: When two 

 atoms of carbon are united by a single bond, each is capable of 

 free rotation in either direction about the common axis ; and iso- 

 mers may be recognized for those bodies only which cannot be 

 brought into the same configuration by such rotation. But some 

 apparent exceptions aaust not be ignored, especially a marked 

 exception to the principle of free rotation, announced two years 

 ago by Auwers and V. Meyer. 



Again, using the tetrahedron as the symbol of the carbon atom, 

 we may conceive two such forms united on a common edge, with 

 hydrogen at the four free corners, to represent the molecule of 

 ethylene (C0H4). In like manner, acetylene derivatives may be 

 represented by two tetrahedrons with a common face. 



Finally the theory of rings was discussed. A campaign is thus 

 being conducted towards the stronghold of atomic mysteries. 



The current theories of stereochemistry or geometrical isomer- 

 ism are based upon those residuals of observed facts that find no 

 explanation in the usual doctrine of structural formulas. Any 

 complete bibliography, covering all the experimental evidence 

 that may bear upon this subject, must therefore include all re- 

 actions or properties that aid us in determining the constitution of 

 the many compounds capable of appearing in geometrical isomers. 

 In the list appended to Professor Warder's paper an attempt is 

 made to include those papers only that may be most useful to 

 chemists or physicists desiring to acquaint themselves with the 

 history of the stereochemical conception, its originators, sup- 

 porters, and opposers. The full value of Professor Warder's 

 paper cannot be appreciated without the use of the many dia- 

 grams which are not available for our use. 



NOTES AND NEWS. 



The pressure of natural-gas wells in Indiana and Ohio is 

 steadily diminishing, the diminution having already amounted to 

 between 30 and 40 per cent. Professor Orton urges the impera- 

 tive necessity of cities and States taking action to restrict 

 wasteful use of gas; but even the strictest regulations, he says, 

 cannot prevent the exhaustion of the supply in a few years. In 

 this connection, says the Engineering and Mining Journal, it is 

 interesting to note that the Pennsylvania Company has taken the 

 step of refusing to sell natural gas in Erie, Penn., except by me- 

 tre, charging 23-1 cents per 1,000 cubic feet, in order to prevent 

 waste of the gas. No factories are to be furnished at any point 

 on its line, as all the gas will be used for domestic purposes. 



— The American Folk-Lore Society will hold its annual meeting 

 in New York City on Nov. 38 and 29, these dates being the 

 Friday and Saturday following Thanksgiving Day. The sessions 

 will be held at Columbia College, in rooms kindly placed at the 

 disposition of the society by President Low. Last year the annual 



